Document conveyance apparatus and image forming apparatus

ABSTRACT

Provided is a document conveyance apparatus that conveys a document along a document conveyance path including a reading position at which an image on a surface of the document is read, the document conveyance apparatus including: a hardware processor; an end detector that detects an angle of a corner portion of a front edge of the document; and an inclination detector that detects an amount of inclination of the front edge, wherein, in a case where it has been determined that the corner portion of the front edge includes a right angle portion on the basis of information obtained from the end detector, the hardware processor determines the amount of inclination of the front edge obtained from the inclination detector as an amount of inclination of the document, and performs inclination correction of the image read at the reading position.

The entire disclosure of Japanese patent Application No. 2017-026077, filed on Feb. 15, 2017, is incorporated herein by reference in its entirety.

BACKGROUND Technological Field

The present invention relates to an image forming apparatus for forming an image by an electrophotographic method and a document conveyance apparatus used for the same. The image forming apparatus includes a recording apparatus, a display apparatus, and an electrophotography apparatus such as a digital copier, a facsimile machine, and a printer, regardless of color or monochrome.

Description of the Related Art

JP 2012-085232 A, JP 2016-036065 A, and JP 2015-170927 A each disclose an invention relating to an image processing apparatus.

The image processing apparatus disclosed in JP 2012-085232 A adopts a technique of determining the orientation of a partial image of character attribute and, in the case where the orientation is not correct, rotating the partial image of character attribute so that the orientation becomes correct.

In JP 2016-036065 A, a reading apparatus extracts edges of a document from image data, and obtains inclination α of a leading edge Et of the document and inclination β of a trailing edge Eb of the document on the basis of the extracted edge, and, in the case where the difference between the inclination α and the inclination β is larger than a rotational skew threshold value, a scanner determines that rotational skew in which the inclination of the document changes in accordance with conveyance of the document has occurred. Thereafter, a technique in which the inclination of the leading edge and the inclination of the trailing edge are compared, and at least one of determining a takeout range and determining the amount of rotation is executed on the basis of the inclination with a smaller inclination angle is adopted.

The image reading apparatus disclosed in JP 2015-170927 A includes a document type and/or document discriminator, and selects an appropriate document inclination detection method in accordance with the discriminated document type and/or document. JP 2015-170927 A discloses a technique in which a document region is detected by selecting a reliable end which is a predetermined document end as a target for detection of the position of the document and detecting the inclination of the document and/or the position of the document with reference to the selected reliable end.

In the related art, the inclination of a read image is corrected with reference to an edge portion of the leading end of the document. However, in the case where a user defines an edge on the cut section side of a document cut by the user as the front end of the document, if the cut section is oblique (if the leading end and the trailing end of the document are not parallel), inclination correction is performed with reference to the oblique cut section, and the read image is inclined (an example of a cut document).

As disclosed in JP 2012-085232 A, there is also a method of correcting the inclination with reference to characters in the image by using an optical character recognition (OCR) function. However, there is no guarantee that the characters and the inclination of the document match.

In the technique disclosed in JP 2016-036065 A, inclination of an edge including an angle and a direction. corresponding to a direction orthogonal to a document conveyance direction is detected. A case of a regular size sheet is assumed, and, for example, in the case of using a book as a document, the binding direction is different depending on whether the characters are arranged vertically or horizontally, and at which of the leading end and the trailing end a cut section is set in the conveyance direction is unknown. Furthermore, in the case where one of the leading end or the trailing end is a cut end and the inclination of the read image on the cut end side is small, the inclination is corrected with reference to the cut end.

In the technique disclosed in JP 2015-170927 A, a document type and a document shape are detected from a scanned image, and an inclination correction method is selected on the basis of a detection result. However, since the process is started after all images have been read once, the process takes time, and thus is unsuitable for high-speed reading of a large number of documents.

SUMMARY

An object of the present invention set on the basis of the problems above is to provide a document conveyance apparatus and an image forming apparatus which enable determining whether a document set on a tray by a user is inclined due to conveyance or an end portion (cut section) of a document is oblique, and on the basis of the result of determination, performing appropriate inclination correction in high-speed reading of a large number of documents irrespective of the direction in which the user has set the documents.

To achieve the abovementioned object, according to an aspect of the present invention, there is provided a document conveyance apparatus that conveys a document along a document conveyance path, the document conveyance path including a reading position at which an image on a surface of the document is read, and the document conveyance apparatus reflecting one aspect of the present invention comprises: a hardware processor; an end detector that is disposed in the document conveyance path and detects an angle of a corner portion of a front edge of the document, the front edge being on a front side in a conveyance direction of the document as viewed in the conveyance direction; and an inclination detector that detects an amount of inclination of the front edge with respect to the conveyance direction, wherein, in a case where it has been determined that the corner portion of the front edge includes a right angle portion on the basis of information obtained from the end detector, the hardware processor determines the amount of inclination of the front edge obtained from the inclination detector as an amount of inclination of the document, and performs, with reference to the front edge, inclination correction of the image read at the reading position.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention:

FIG. 1 is a perspective view showing a configuration of an image forming apparatus according to an embodiment;

FIG. 2 is a block diagram showing a configuration of the image forming apparatus according to the embodiment;

FIG. 3 is a diagram showing an internal configuration of a scanner unit and an automatic document feeder (ADF) unit according to the embodiment;

FIG. 4 is a diagram showing a left binding document;

FIG. 5 is a diagram showing a right binding document;

FIG. 6 is a diagram showing a document bound by using staples;

FIG. 7 is a diagram showing a case where a cut section (cutting line) of the document is oblique;

FIG. 8 is a schematic diagram showing arrangement positions of sensors with respect to a conveyance center line of a conveyed document;

FIG. 9 is a diagram showing an arrangement relationship between a conveyed document and each sensor position;

FIG. 10 is a schematic diagram showing a detection method of a conveyance state of a conveyed document, and is a diagram showing a case where a cut section of the document is orthogonal;

FIG. 11 is a diagram schematically showing detection timings of inclination sensors and an end detection sensor in the case of the document shown in FIG. 10;

FIG. 12 is a schematic diagram showing a detection method of a conveyance state of a conveyed document, and is a diagram showing a case where a cut section of the document on the rear side is inclined;

FIG. 13 is a diagram schematically showing detection timings of the inclination sensors and the end detection sensor in the case of the document shown in FIG. 12;

FIG. 14 is a schematic diagram showing a detection method of a conveyance state of a conveyed document, and is a diagram showing a case where a cut section of the document on the front side is inclined;

FIG. 15 is a diagram schematically showing detection timings of the inclination sensors and the end detection sensor in the case of the document shown in FIG. 14;

FIG. 16 is a diagram schematically showing an inclination correction flow for an image using the inclination sensors and the end detection sensor shown in FIGS. 12 to 15;

FIG. 17 is a schematic diagram showing a detection method of a conveyance state of a conveyed document, and is a diagram showing a case where the conveyed document is inclined and the cut section of the document is orthogonal;

FIG. 18 is a diagram schematically showing detection timings of the inclination sensors and the end detection sensor in the case of the document shown in FIG. 17;

FIG. 19 is a schematic diagram showing a detection method of a conveyance state of a conveyed document, and is a diagram showing a case where the conveyed document is inclined and the cut section of the document on the rear side is inclined;

FIG. 20 is a diagram schematically showing detection timings of the inclination sensors and the end detection sensor in the case of the document shown in FIG. 19;

FIG. 21 is a schematic diagram showing a detection method of a conveyance state of a conveyed document, and is a diagram showing a case where the conveyed document is inclined and the cut section of the document on the front side is inclined;

FIG. 22 is a diagram schematically showing detection timings of the inclination sensors and the end detection sensor in the case of the document shown in FIG. 21;

FIG. 23 is a diagram showing another position of the end detection sensor;

FIG. 24 is a diagram showing yet another position of the end detection sensor;

FIG. 25 is a schematic diagram showing a detection method of a conveyance state of a conveyed document, and is a diagram showing a case where a cut section of the document of an upper end is inclined; and

FIG. 26 is a diagram schematically showing detection timings of the inclination sensors and the end detection sensor in the case of the document shown in FIG. 25.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an image forming apparatus according to one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. In the embodiment described below, when referring to the number, amount, etc., the scope of the present invention is not necessarily limited to the number, amount, etc. unless otherwise stated. Identical parts and equivalent parts are denoted by the same reference numerals, and redundant explanations may not be repeated. In the drawings, illustration is not given in accordance with the ratio of the actual dimensions, and is given at some parts by changing the ratio for the sake of easier understanding of the structure.

Examples of the image forming apparatus include a multi-function printer (MFP), a facsimile machine, or a copier. The MFP has a scanner function, a copying function, a function as a printer, a facsimile function, a data communication function, and a server function. In addition, a document conveyance apparatus is an automatic document feeder (ADF) unit provided in the image forming apparatus.

[Configuration of Image Forming Apparatus 1]

Referring to FIG. 1 to FIG. 3, an image forming apparatus 1 of the present embodiment will be described. FIG. 1 is a perspective view showing a configuration of the image forming apparatus 1, FIG. 2 is a block diagram showing a configuration of the image forming apparatus 1, and FIG. 3 is a diagram showing an internal configuration of a scanner unit and the ADF unit.

Referring to FIG. 1, the image forming apparatus 1 is an MFP. The image forming apparatus 1 includes a controller 10, an image former 20, a sheet feeder 30, a scanner unit 40, an ADF (Auto Document Feeder) unit 50 serving as a document conveyance apparatus, and an operation panel 60. The controller 10, the image former 20, and the sheet feeder 30 are located in the center of the image forming apparatus 1. The scanner unit 40 and the ADF unit 50 are located in an upper portion the image forming apparatus 1. The operation panel 60 is located on a front upper surface of the image forming apparatus 1.

Referring to FIG. 2, the controller 10 includes a central processing unit (CPU) 11, a read only memory (ROM) 12, a random access memory (RAM) 13, a communication interface (I/F) 14, an image data storage 15, and a document size storage 16. The CPU 11, the ROM 12, the RAM 13, the communication I/F 14, the image data storage 15, and the document size storage 16 are connected to one another.

The CPU 11 controls the overall operation of the image forming apparatus 1. The ROM 12 stores a control program executed by the CPU 11. The RAM 13 is a work memory for the CPU 11. The communication I/F 14 transmits and receives various kinds of information to and from external devices (not shown) through a network or the like. The image data storage 15 stores image data read by the scanner unit 40 and the like. The document size storage 16 stores the size of a document measured by the ADF unit 50 and the size of a document set through the operation panel 60.

Roughly speaking, the image former 20 is constituted by a toner image former and a fixing device. The image former 20 forms an image on a sheet by, for example, an electrophotographic method. The image former 20 is configured to be able to form a color image on a sheet by combining images of four colors in a so-called tandem system.

The toner image former includes photosensitive members provided for respective colors of cyan (C), magenta M, yellow Y, and black K, an intermediate transfer belt to which toner images are transferred from the photosensitive members, and a transfer unit that transfers (secondary transfer) an image from the intermediate transfer belt to a sheet.

The fixing device includes a heating roller and a pressurizing roller. The fixing device conveys a sheet on which a toner image has been formed by the heating roller and the pressurizing roller while nipping the sheet therebetween, and heats and pressurizes the sheet. As a result, the fixing device melts the toner adhered to the sheet, fixes the toner on the sheet, and thus forms an image on the sheet.

The sheet feeder 30 is constituted by a sheet feeding roller, a conveyance roller, a motor for driving these, and the like. The sheet feeder 30 feeds a sheet from a sheet feeding cassette and conveys the sheet inside the housing of the image forming apparatus 1. The sheet feeder 30 discharges the sheet on which the image has been formed from the image forming apparatus 1 to a sheet discharge tray or the like. The scanner unit 40 reads an image of a document and generates image data of the document.

The ADF unit 50 sends documents (an example of sheets) one by one to the scanner unit 40. The ADF unit 50 includes a document conveyance motor 51, a back surface reader 52 provided in the case of double-sided simultaneous reading at the time of document conveyance, a document size detection sensor 53, a pre-document reading sensor 54, an inclination sensor (R) 55, an inclination sensor (F) 56, and an end detection sensor 57. The document conveyance motor 51 operates under the control of the CPU 11.

The document conveyance motor 51 includes an upstream roller driving motor and a downstream roller driving motor. The upstream roller driving motor drives a sheet feeding roller 154 (FIG. 3). The downstream roller driving motor drives conveyance rollers 155, 156, 157, 158 and a sheet discharge roller 159 (FIG. 3). The document size detection sensor 53 detects the size of the document placed on a document tray 151 (FIG. 3). The pre-document reading sensor 54 detects the presence or absence of the document along a conveyance path, and is constituted by an optical or mechanical sensor.

The detailed arrangement of the inclination sensor (R) 55, the inclination sensor (F) 56, and the end detection sensor 57 will be described later. Optical or mechanical sensors are used for the inclination sensor (R) 55, the inclination sensor (F) 56, and the end detection sensor 57, similarly to the pre-document reading sensor 54.

More specifically, the inclination sensor (R) 55 and the inclination sensor (F) 56 detect passage of an end portion of the sheet. Specifically, for example, one photoelectric sensor is used to detect the passage of the end portion of the sheet by blocking a light beam. The end detection sensor 57 detects the shape of a corner portion of the sheet. Specifically, a photoelectric sensor arranged in a matrix is used to determine whether or not the corner portion of the sheet includes a right angle depending on a light blocking state.

The operation panel 60 displays various information and accepts various operations. The operation panel 60 includes a start button 61 for starting various jobs such as a reading job and a copying job.

Referring to FIG. 3, the ADF unit 50 is positioned above the scanner unit 40. The scanner unit 40 is capable of reading a document placed on a document table 141 and reading a document sent from the ADF unit 50.

The scanner unit 40 includes the document table 141, a light source 142, mirrors 143 a, 143 b, and 143 c, and a charge coupled device (CCD) 144. Light emitted from the light source 142 and reflected by the surface of a document is reflected by each of the mirrors 143 a, 143 b, and 143 c, and is incident on the CCD 144. Thus, the scanner unit 40 reads the document.

The ADF unit 50 includes the document tray 151, a sheet discharge tray 152, a pickup roller 153, the sheet feeding roller 154, the conveyance rollers 155, 156, 157, and 158, the sheet discharge roller 159, and a contact image sensor (CIS) 160. A document to be read is placed or the document tray 151. A document size detection sensor 53 for mechanically detecting the document is provided on the upper surface of the document tray 151, and the size of the placed document is measured on the basis of a detection result of the document size detection sensor 53. The document whose image has been read is discharged from the ADF unit 50 onto the sheet discharge tray 152.

A conveyance path TR connecting the document tray 151 to the sheet discharge tray 152 is provided in the ADF unit 50. The pickup roller 153, the sheet feeding roller 154, the conveyance rollers 155, 156, 157, and 158, and the sheet discharge roller 159 are arranged in this order from the document tray 151 to the sheet discharge tray 152 along the conveyance path TR. A reading position RP is provided between the conveyance roller 156 and the conveyance roller 157. The CIS 160 is provided between the conveyance roller 157 and the conveyance roller 158.

The ADF unit 50 sequentially supplies documents placed on the document tray 151 one by one to the conveyance path TR by the pickup roller 153 and the sheet feeding roller 154. The ADF unit 50 performs registration correction on a document supplied to the conveyance path TR by using the conveyance roller 155. The ADF unit 50 conveys the document supplied to the conveyance path TR along the conveyance path TR to the reading position RP by the conveyance rollers 155 and 156.

The scanner unit 40 reads a front surface of the conveyed document at the reading position RP. Next, the ADF unit 50 conveys the document whose front surface has been read to the CIS 160 along the conveyance path TR by the conveyance roller 157. The scanner unit 40 reads a back surface of the conveyed document by the CIS 160. Thereafter, the ADF unit 50 conveys the document along the conveyance path TR to a discharge port by the conveyance roller 158, and discharges the document onto the sheet discharge tray 152 by the sheet discharge roller 159.

(Inclination Detection of Document)

The inclination sensor (R) 55, the inclination sensor (F) 56, and the end detection sensor 57 are arranged in the conveyance path TR. Hereinafter, a method for determining whether the document set on the document tray by the user is inclined due to conveyance or an end portion of the document (cut section) is oblique using this arrangement and these sensors will be described below with reference to drawings.

Referring to FIG. 4 to FIG. 7, cutting modes of the document will be described. FIG. 4 shows a document B1 bound on the left, FIG. 5 shows a document B2 bound on the right, FIG. 6 shows a document bound by using staples, and FIG. 7 shows a case Where the cut section (cutting line) of the document is oblique.

Normally, in the case of the document B1 bound on the left shown in FIG. 4, the document is opened from the right side to the left side. Characters are arranged horizontally. In the case of the document 132 bound on the right shown in FIG. 5, the document is opened from the left side to the right side. Characters are arranged vertically. As shown in FIG. 6, in the document using staples ST, cutting is performed such that portions corresponding to the staples ST are cut off. Referring to FIG. 7, the case where the cut section (cutting line) S1 of a document P11 is oblique will be shown.

Referring to FIG. 8 and FIG. 9, description will be given for each sensor position provided in the conveyance path TR. FIG. 8 is a schematic diagram showing the positions of the sensors with respect to a conveyance center line CL of the conveyed document, and FIG. 9 is a diagram showing the arrangement relationship between the conveyed document and each sensor position.

Referring to FIG. 8, an arrow in FIG. 8 corresponds a document conveyance direction F1. In the case of the image forming apparatus 1 shown in FIG. 1, the left side in FIG. 8 is the rear side of the apparatus and the right side in FIG. 8 is the front side of the apparatus when viewed in the document conveyance direction F1 in the ADF unit 50.

As shown in FIG. 8, a pre-document reading sensor 54 is disposed at a position displaced by an amount S1 toward the front side of the apparatus with respect to the conveyance center line CL. With respect to the conveyance center line CL, the inclination sensor (R) 55 is disposed at a position displaced by an amount S2 toward the rear side of the apparatus, and the inclination sensor (F) 56 is disposed at a position displaced by an amount S3 toward the front side of the apparatus.

In the present embodiment, as an example, the pre-document reading sensor 54 is disposed at a position of 6.0 mm as the amount S1, the inclination sensor (R) 55 and the inclination sensor (F) 56 are disposed at positions of 87.0 mm as the amounts S2 and S3. Further, as shown in FIG. 9, the end detection sensor 57 is disposed in the vicinity of the inclination sensor (F) 56 disposed on the front side of the device.

As shown in FIG. 3, regarding the positions of the inclination sensor (R) 55, the inclination sensor (F) 56, and the end detection sensor 57 in the ADF unit 50, the inclination sensor (R) 55 and the inclination sensor (F) 56 are arranged on substantially the same line as the pre-document reading sensor 54 in a direction orthogonal to the document conveyance direction F1. When viewed along the conveyance direction F1 of the document, the end detection sensor 57 is disposed downstream of the inclination sensor (R) 55 and the inclination sensor (F) 56 and upstream of the reading position RP.

As described above, the inclination sensor (R) 55 and the inclination sensor (F) 56 detect passage of an end portion of the sheet. The end detection sensor 57 detects the shape of a corner portion of the sheet.

Referring to FIGS. 10 to 16, a method for detecting the conveyance state of the conveyed document will be described. FIG. 10 shows a case of a document P10 with an orthogonal cut section, and FIG. 11 is a diagram schematically showing detection timings of the inclination sensor (R) 55, the inclination sensor (F) 56, and the end detection sensor 57 in the case of the document P10 shown in FIG. 10. The document P10 may be bound on the right side or bound on the left side.

FIG. 12 shows a case of a document P11 whose cut section on the rear side is inclined, and FIG. 13 is a diagram schematically showing detection timings of the inclination sensor (R) 55, the inclination sensor (F) 56, and the end detection sensor 57 in the case of the document P11 shown in FIG. 11. The document P11 is usually bound on the right side.

FIG. 14 shows a case of a document P12 whose cut section on the front side is inclined, and FIG. 15 is a. diagram schematically showing detection timings of the inclination sensor (R) 55, the inclination sensor (F) 56, and the end detection sensor 57 in the case of the document P12 shown in FIG. 14. The document P12 is usually bound on the left side.

FIG. 16 is a diagram schematically showing an inclination correction flow for an image using the inclination sensor (R) 55, the inclination sensor (F) 56, and the end detection sensor 57 shown in FIGS. 12 to 15.

Referring to FIGS. 10, 11 and 16, the document P10 is conveyed (S10), and it is detected by the end detection sensor 57 that a front corner portion C1 of the document P11 includes a right angle (S20 and S30). Next, as a front end P10 f and a rear end P10 r of the document P10 sequentially pass by the inclination sensor (R) 55 and the inclination sensor (F) 56, widths W11 and W12 of the document P10 along the conveyance direction being the same is detected. As a result, it is detected that a cut section S1 of the document P10 is orthogonal, and the amount of inclination of the front end P10 f is detected (S40). Next, inclination correction is performed on a read image with reference to the front side of the document P10 (S50). Specifically, in the case of this document. P10, the inclination correction of the image is zero.

Referring to FIGS. 12, 13 and 16, the document P11 is conveyed (S10), and it is detected by the end detection sensor 57 that a front corner portion C1 of the document P11 includes a right angle (S20 and S30). Next, as a front end P11 f and a rear end P11 r of the document P11 sequentially pass by the inclination sensor (R) 55 and the inclination sensor (F) 56, widths W11 and W12 of the document P11 along the conveyance direction being different is detected.

However, the front end P11 f of the document P11 passes by the inclination sensor (R) 55 and the inclination sensor (F) 56 at the same time. As a result, it is detected that the front end P11 f of the document P11 is orthogonal, and the amount of inclination of the front end P11 f is detected (S40). Next, the inclination correction of the read image is performed with reference to the front side of the document P11 (S50). Specifically, in the case adds document P11, the inclination correction of the image is zero.

Referring to FIGS. 14, 15 and 16, the document P12 is conveyed (S10), and it is detected by the end detection sensor 57 that a front corner portion C1 of the document P12 does not include a right angle (S20 and S30). Next, as a front end P12 f and a rear end P12 r of the document P12 sequentially pass by the inclination sensor (R) 55 and the inclination sensor (F) 56, widths W11 and W12 of the document P12 along the conveyance direction being different is detected.

However, the rear end P12 r of the document P12 passes though the inclination sensor (R) 55 and the inclination sensor (F) 56 at the same time. Further, the end detection sensor 57 detects that a corner portion C2 on the rear side of the document P12 includes a right angle (S60). As a result, it is determined that the rear end P12 r is orthogonal although the front end P12 f of the document P12 is not orthogonal (S70). Next, inclination correction of the read image is performed with reference to the rear side of the document P12 (S80). Specifically, in the case adds document P12, the inclination correction of the image is zero.

If neither of the corner portions on the front side and the back side of the document is orthogonal, conveyance of the document is stopped (S90).

In FIGS. 10 to 12 described above, a case where edges on the front side and rear side of the apparatus of the documents P10, P11, and P12 are parallel to the document conveyance direction F1 has been described. Next, referring to FIG. 17 to FIG. 22, a case where the edges on the front side and rear side of the apparatus are not parallel to the document conveyance direction F1 will be described.

FIG. 17 shows a case of the document P10 with an orthogonal cut section, and FIG. 18 is a diagram schematically showing detection timings of the inclination sensor (R) 55, the inclination sensor (F) 56, and the end detection sensor 57 in the case of the document P10 shown in FIG. 17. The document P10 may be bound on the right side or bound on the left side.

FIG. 19 shows a case of the document P11 whose cut section on the rear side is inclined, and FIG. 20 is a diagram schematically showing detection timings of the inclination sensor (R) 55, the inclination sensor (F) 56, and the end detection sensor 57 in the case of the document P11 shown in FIG. 19. The document P11 is usually bound on the right side.

FIG. 21 shows a case of the document P12 whose cut section on the front side is inclined, and FIG. 22 is a diagram schematically showing detection timings of the inclination sensor (R) 55, the inclination sensor (F) 56, and the end detection sensor 57 in the case of the document P12 shown in FIG. 21. The document P12 is usually bound on the left side.

Referring to FIGS. 17, 18 and 16, the document P10 is conveyed (S10), and it is detected by the end detection sensor 57 that a front corner portion C1 of the document P10 includes a right angle (S20 and S30). Next, as a front end P10 f and a rear end P10 r of the document P10 sequentially pass by the inclination sensor (R) 55 and the inclination sensor (F) 56, widths W11 and W12 of the document P10 along the conveyance direction being the same is detected.

As a result, it is detected that the front end P11 f of the document P11 is orthogonal, and the amount of inclination of the front end P11 f is detected (S40). Next, inclination correction is performed on a read image with reference to the front side of the document P10 (S50). Specifically, in the case of this document P10, the inclination of the image is obtained from the time difference of passage of the front end P10 f between the inclination sensor (R) 55 and the inclination sensor (F) 56.

Referring to FIGS. 19, 20 and 16, the document P11 is conveyed (S10), and it is detected by the end detection sensor 57 that a front corner portion C1 of the document P11 includes a right angle (S20 and S30). Next, as a front end P11 f and a rear end P11 r of the document P11 sequentially pass by the inclination sensor (R) 55 and the inclination sensor (F) 56, widths W11 and W12 of the document P11 along the conveyance direction being different is detected.

However, since the corner portion C1 on the front side of the document P11 includes a right angle, it is detected that the front end P11 f of the document P11 is orthogonal, and the amount of inclination of the front end P11 f is detected (S40). Next, the inclination correction of the read image is performed with reference to the front side of the document P11 (S50). Specifically, in the case of this document P11, the inclination of the image is obtained from the time difference of passage of the front end P11 f between the inclination sensor (R) 55 and the inclination sensor (F) 56.

Referring to FIGS. 21, 22 and 16, the document P12 is conveyed (S10), and it is detected by the end detection sensor 57 that a front corner portion C1 of the document P12 does not include a right angle (S20 and S30). Next, it is detected that a corner portion C2 of the document P12 on the rear side includes a right angle (S60). Next, as a front end P12 f and a rear end P12 r of the document P12 sequentially pass by the inclination sensor (R) 55 and the inclination sensor (F) 56, widths W11 and W12 of the document P12 along the conveyance direction being different is detected. However, the end detection sensor 57 detects that a corner portion C2 on the rear side of the document P12 includes a right angle (S60).

As a result, it is determined that the rear end P12 r is orthogonal although the front end P12 f of the document P12 is not orthogonal (S70). Next, inclination correction of the read image is performed with reference to the rear side of the document P12 (S80). Specifically, in the case of this document P12, the inclination of the image is obtained from the time difference of passage of the front end P12 f between the inclination sensor (R) 55 and the inclination sensor (F) 56.

If neither of the corner portions on the front side and the back side of the document is orthogonal, conveyance of the document is stopped (S90).

As described above, the image forming apparatus 1 according to the present embodiment determines whether the document set on the tray by the user is inclined due to conveyance or an end portion of the document (cut section) is oblique, and, in the case where it is determined that the front end side of the document includes a right angle, the amount of inclination is determined immediately with reference to the leading end of the document. Thus, the amount of inclination can he determined before the image reading is completed, the time required by the correction process is reduced, and appropriate inclination correction can be performed for high-speed reading of a large number of documents.

To be noted, although the end detection sensor 57 is disposed on the front side of the apparatus in the image forming apparatus 1 described above, the end detection sensor 57 may be disposed on the rear side of the apparatus as shown in FIG. 23. Further, as shown in FIG. 24, the end detection sensor 57 may be disposed to extend from the rear side to the front side of the apparatus.

Further, although a case where cut surface is disposed on the front side or the rear side of the document P10, P11, or P12 in the conveyance direction has been described, whether the document set on the tray by the user is inclined due to conveyance or the end portion of the document (cut section) is oblique can be determined similarly also in the case of a document P21 whose cut section is disposed on the rear side of the apparatus as shown in FIGS. 25 and 26.

Furthermore, in the image forming apparatus 1 described above, when reading not only an image on the front surface of the document but also an image on the back surface of the document, image correction similar to the image correction performed on the image on the front surface may be performed on the image on the back surface.

Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims. The scope of the present invention is intended that all modifications within meaning and scope equivalent to the claims are included. 

What is claimed is:
 1. A document conveyance apparatus that conveys a document along a document conveyance path, the document conveyance path including a reading position at which an image on a surface of the document is read, the document conveyance apparatus comprising: a hardware processor; an end detector that is disposed in the document conveyance path and detects an angle of a corner portion of a front edge of the document, the front edge being on a front side in a conveyance direction of the document as viewed in the conveyance direction; and an inclination detector that detects an amount of inclination of the front edge with respect to the conveyance direction, wherein, in a case where it has been determined that the corner portion of the front edge includes a right angle portion on the basis of information obtained from the end detector, the hardware processor determines the amount of inclination of the front edge obtained from the inclination detector as an amount of inclination of the document, and performs, with reference to the front edge, inclination correction of the image read at the reading position.
 2. The document conveyance apparatus according to claim 1, wherein in a case where it has been determined that the corner portion of the front edge does not include a right angle portion on the basis of the information obtained from the end detector, the hardware processor performs control such that the end detector detects an angle of a corner portion of a rear edge of the document, the rear edge being on a rear side in the conveyance direction as viewed in the conveyance direction, and that the inclination detector detects an amount of inclination of the rear edge with respect to the rear edge, and in a case where it has been determined that the corner portion of the rear edge includes a right angle portion on the basis of information obtained from the end detector, the hardware processor determines the amount of inclination of the rear edge obtained from the inclination detector as the amount of inclination of the document, and performs, with reference to the rear edge, inclination correction of the image read at the reading position.
 3. The document conveyance apparatus according to claim 2, wherein, in a case where it has been determined that neither of the corner portion of the front edge of the document nor the corner portion of the rear edge of the document includes a right angle portion on the basis of the information obtained from the end detector, the hardware processor stops conveyance of the document.
 4. The document conveyance apparatus according to claim 1, wherein, in a case of reading both of an image on a front surface of the document and an image on a back surface of the document, the hardware processor performs the same inclination correction on the image on the back surface as on the image on the front surface.
 5. An image forming apparatus comprising: a document conveyance apparatus that conveys a document along a document conveyance path, the document conveyance path including a reading position at which an image on a surface of the document is read; and an image former that forms an image on the basis of the image read by the document conveyance apparatus, wherein the document conveyance apparatus includes: a hardware processor; an end detector that is disposed in the document conveyance path and detects an angle of a corner portion of a front edge of the document, the front edge being on a front side in a conveyance direction of the document as viewed in the conveyance direction; and an inclination detector that detects an amount of inclination of the front edge with respect to the conveyance direction, and in a case where it has been determined that the corner portion of the front edge includes a right angle portion on the basis of information obtained from the end detector, the hardware processor determines the amount of inclination of the front edge obtained from the inclination detector as an amount of inclination of the document, and performs, with reference to the front edge, inclination correction of the image read at the reading position.
 6. The image forming apparatus according to claim 5, wherein in a case where it has been determined that the corner portion of the front edge does not include a right angle portion on the basis of the information obtained from the end detector, the hardware processor performs control such that the end detector detects an angle of a corner portion of a rear edge of the document, the rear edge being on a rear side in the conveyance direction as viewed in the conveyance direction, and that the inclination detector detects an amount of inclination of the rear edge with respect to the rear edge, and in a case where it has been determined that the corner portion of the rear edge includes a right angle portion on the basis of information obtained from the end detector, the hardware processor determines the amount of inclination of the rear edge obtained from the inclination detector as the amount of inclination of the document, and performs, with reference to the rear edge, inclination correction of the image read at the reading position.
 7. The image forming apparatus according to claim 6, wherein, in a case where it has been determined that neither of the corner portion of the front edge of the document nor the corner portion of the rear edge of the document includes a right angle portion on the basis of the information obtained from the end detector, the hardware processor stops conveyance of the document.
 8. The image forming apparatus according to claim 5, wherein, in a case of reading both of an image on a front surface of the document and an image on a back surface of the document, the hardware processor performs the same inclination correction on the image on the back surface as on the image on the front surface. 